Touch screens are present in many different types of common modern electronic devices, such as smart phones, tablet computers, portable music and video devices, personal digital assistants, portable gaming devices, and so on. In these electronic devices the touch screen is part of the user interface of the device. The touch screen typically includes a touch display and sensors, and a touch controller is coupled to the touch screen. The sensors are typically some sort of transparent sensor array, such as an ultrasonic, resistive, vibration, or capacitive sensor array, or a combination thereof, which is attached to or formed as an integral part of the touch display. When a user touches a surface of touch display and thereby touches the sensor array, either with a finger or a stylus, for example, the sensor array generates corresponding electronic sensor signals that are provided to the touch controller. From these sensor signals, the touch controller determines the type of “touch event” made by the user on the touch screen and provides this information to processing circuitry in the electronic device. The processing circuitry operates in response to this information to allow a user to control the electronic device or an application running on the processing circuitry through these touches of the touch screen.
Current touch screens also provide three-dimensional sensing, where the sensing is termed “three-dimensional” because user or “interface inputs” in the form of a user's finger, stylus, or other device being present above but not in contact with the surface of the touch display can also be detected, along with interface inputs in the form of “touch events” directly on the surface of the touch display. The term “interface input” is used herein to refer generally to all types of actions by a user's finger or other device that can be sensed by a touch screen. The terms “touch event” or “touch” are used to mean an interface input, whether stationary or moving, where the user's finger or other device is directly in contact with the surface of the touch display. The terms “hover event” or simply “hover” are used to mean an interface input where the user's finger or other device is stationary or moving (e.g., during a hover zoom interface input the user's fingers would be moving) and within a certain “sensing range” SR from the surface of the touch display, but is not actually in contact with or touching the surface. The sensing range SR is a distance orthogonal to the surface of the touch display within which the user' finger or other device will be reliably sensed by the touch screen, as will be appreciated by those skilled in the art. Finally, the terms “gesture event” or “gesture” are used to mean an interface input where the user's finger or other device is moving in a predefined constrain and is within the sensing range SR of the touch display. Examples of predefined constrains are the user's finger moving faster than normal over a specified distance and the user's finger drawing, in air, a certain pattern, such as a ‘Z-shaped’ pattern. Thus, for both gesture and hover events the user's finger or other device is not actually in contact with or touching the surface of the touch display. Finally, note that for the sake of brevity, in the remainder of the present application a user's finger will be used to describe the device that is being sensed by the touch screen. One skilled in the art will appreciate, however, that any suitable type of device, such as a stylus, tablet pen, or other type of device, may be used to generate the interface input (i.e., touch event, hover event, or gesture event) that is being detected.
In both hover and gesture events, the user's finger is within the sensing range SR above the surface of the touch display and the type of event (i.e., either hover or gesture) is differentiated by the predefined constrains. The touch screen and controller must, of course, be able to reliably distinguish between these two types of events and detect whether the event is a hover event or a gesture event. One approach to doing so is for the touch screen to utilize different sensing technologies to sense hover and gesture events. For example, one such approach utilizes capacitive sensing technology to detect hover events and infrared (IR) sensing technology to detect gesture events. With this approach, the touch screen obviously must include both capacitive sensors and IR sensors. There is a need for improved methods, circuits, and systems for reliably sensing and distinguishing between hover and gesture events with a touch screen.